The central goal of Project 5 is to understand the interplay between fluid shear stress, cell morphology, and L-selectin expression on the dynamics of neutrophil tethering and rolling on the endothelium. We will use a combination of state-of-the-art computational simulations of receptor-mediated cell adhesion under flow, in vitro experiments with isolated human neutrophils and neutrophil-like cell lines in well-deflned fluid shear environments, and collaborative invesfigafion with other projects. The mulfiparticle adhesive dynamics simulafion developed by the PI, enables the invesfigafion of previously unaddressed problems such as the influence of non-spherical shape on the physics of leukocyte rolling, and computational and experimental study of L-selecfin shedding and mechanosensing. The multitude of physical determinants combining to control neutrophil inflammatory recruitment, including receptor expression, activation state, cell shape, local flow environment, and cell-cell collisions are highly complex and nonlinear and so we have taken a systematic integrated engineering approach to elucidate these behaviors. The proposed work is organized around three specific aims. Aim 1: Selecfin-Mediated Tethering and Rolling of Activated Leukocytes: In this aim we will use mulfiparticle adhesive dynamics simulafions of acfivated cell shapes, and detailed analysis of in vivo observations of activated cell rolling, to study the dynamics of non-spherical cell adhesion. Aim 2: Mechanisms of L-Selecfin Mechanotransducfion and Shedding During Rolling. This aim will explore the molecular mechanisms of mechanical shedding in flow chamber experiments with primary neutrophils and an altered neutrophil-like cell line. Aim 3: Shear-Induced Resistance to Activation via Chemoattractant GPCRs. In this aim, we will study the quantitafive dynamics of the shear stress-dependent GPCR-mediated response of neutrophils to fMLP and platelet activating factor (PAF). Together, the proposed research will determine for the first fime how the physics of nonspherical leukocyte shape, and the mechanical response of neutrophil receptors at the single molecule level, influence the dynamics of cell tethering and rolling to selecfin-presenfing endothelium under physiological flow.